1. Field of the Invention
The present invention is related to the iron-tip temperature detector of an electric soldering iron, which detects the current temperature of the iron tip of the soldering iron and issues a signal indicative of such temperature to a temperature controller, so that the temperature of the iron tip can be regulated to a desired value.
2. Description of the Related Art
In order to properly solder electric wiring using an electric soldering iron, it is necessary, in particular, to set and maintain properly the temperature of the iron tip of the soldering iron.
Therefore, electric soldering irons have been provided with a temperature controller that can adjust the temperature of the iron tip.
Such an electric soldering iron is shown in FIG. 7.
In this electric soldering iron 1, a cooling wheel 4 is securely fixed to the tip of grip 2 by way of radiating nut 3. A heater cover 6 covers the iron tip 5 except at the nose of the iron tip 5. A cover nut 7 holds the rear end of iron tip 5 and is screwed onto a male thread formed around the periphery of the central protruding part of the cooling wheel 4.
The iron tip 5 is hollow from the end thereof adjacent grip 2 to near the nose of the iron tip 5. A heater 8 shown in FIG. 6 is inserted in the iron tip. Further, a thermocouple sensor 10, which constitutes the temperature detector, is disposed in the heater 8. That is, the thermocouple sensor 10 is, as shown in FIG. 6, inserted into the heater proper 9 along its axial center, and contact point part 11, which is the recuperator of the sensor, is embedded in a ceramic element 12 provided at the nose of the heater proper 9.
In the conventional electric soldering iron described above, soldering is carried out by supplying electric power to the heater 8, thereby heating the iron tip 5. When using such an electric soldering iron 1, the following temperature regulating process is carried out.
Because contact point part 11 of the thermocouple sensor 10 is fixed securely (by being embedded in ceramic element 12) to the nose of heater 8, the temperature of heater 8 is detected by the thermocouple sensor 10. The detected temperature is converted into a value representing the temperature of iron tip 5 by the temperature controller, and the converted temperature is compared with a reference temperature, namely, the desired iron tip temperature which is preestablished based on the type of soldering. If the converted temperature is lower than the reference temperature, or vice versa, the temperature of iron tip 5 is adjusted by controlling the quantity of the electric power supplied to heater 8.
Therefore, when controlling the temperature of the iron tip of a conventional electric soldering iron 1, the temperature at the iron tip 5 is not directly detected. Rather, the temperature of the heater 8, which is a heating means, is detected, and from the temperature of this heater 8, the temperature of the iron tip 5 is inferred. Then on the basis of the inferred value and said reference temperature, the electric power supplied to heater 8 is adjusted, thereby controlling the temperature of iron tip 5. Because the inferred value may not be the actual temperature of the tip, the tip may be regulated to an improper temperature.
In other words, when using the electric soldering iron 1, the temperature of the iron tip 5 and that of heater 8 maintain nearly a constant relationship when the electric soldering iron is idle, i.e. prior to use. Hence, it is possible to infer a comparatively correct iron-tip temperature from the temperature of heater 8, and the iron-tip temperature can be adjusted in a comparatively correct manner. However, when the actual soldering operation is commenced, the iron tip 5 is cooled by solder and parts to be soldered, and a certain lag occurs before such a lowered iron-tip temperature can be reflected by the heater. During such an actual operation, therefore, the temperature of the iron tip 5 fails to maintain a constant relationship with the temperature of heater 8. Naturally, the temperature, which has been deduced on the basis of the temperature of the heater 8 does not coincide with the actual temperature of the iron tip 5, thereby making it impossible to regulate the temperature of the iron tip 5 to a correct value.
More specifically, a drop in the iron-tip temperature due to solder and parts to be soldered will not be immediately reflected by the temperature of the heater. Therefore, only when the temperature of the iron tip 5 drops considerably, which occurs only after a comparatively long time with respect to the overall soldering operation, will the temperature of the heater 8 drop. Only when the temperature drop is detected will the control system operate to compensate for the temperature drop. Therefore, it is impossible to detect the iron-tip temperature correctly in real time when the iron-tip temperature drops, thereby causing an inferior response by the control system which can result in unsatisfactory soldering.
In particular, because soldering electric parts requires high performance nowadays, it is necessary to adjust the iron-tip temperature of the electric soldering iron with high accuracy in order to solder properly without damaging the electric parts. From this viewpoint, the iron-tip temperature detector of the conventional electric soldering iron poses serious problems.